Drilled shafts are high-capacity cast-in-place deep foundation elements constructed in the soil using an auger. A hole having the design diameter of planned shaft is first drilled to the design depth. Full-length reinforcing steel is then lowered into the hole and the hole is filled with concrete. The finished foundation element resists compressive, uplift and lateral loads.
Designers of drilled shafts and long/large diameter piles do not typically include the tip resistance component in estimating its overall capacity due to excessive deformation needed to achieve such resistance. Post-grouting techniques were developed in response to this demand. These techniques typically entail, after construction of a drilled shaft, pushing grout (a mix of concrete, sand and water) under pressure through tubes embedded in the shaft and passing through the body of the shaft to the bottom of the shaft. This grout occupies the space between the bottom of the shaft and the soil and keeps pushing the soil in an attempt to improve its stiffness and its load carrying capacity.
These post-grouting techniques have been ascribed with several limitations including reliability and repeatability of the technique which has prevented it from being adopted by the construction industry. Thus, a need exists for new techniques and systems that improve drilled shaft/pile end-bearing resistance.